1. Field of the Invention
The present invention relates to a video transmitter, a video transmission method, and a program.
2. Description of the Related Art
In video signal transmission systems between adjacent rooms, diverse wireless transmission systems have been introduced to reduce cables for transmitting video signals from the viewpoint of effective use of indoor spaces. FIG. 15 is a schematic diagram illustrating the constitutions of wireless communication systems in adjacent rooms. In the illustrated example, two rooms, Room 1 and Room 2, are adjacent to each other. In Room 1, CH1 is used to transmit data of a full HD video from a video transmitter Tx1 to a video receiver Rx1. Also, CH2 is used to transmit data of a full HD video from a video transmitter Tx2 to a video receiver Rx2. In Room 2, CH1 is used to transmit data of an SD video from a video transmitter Tx3 to a video receiver Rx3.
As illustrated, when a plurality of rooms are adjacent to each other, communication is assumed to be performed using the same wireless channel in the plurality of rooms. Depending on the material qualities of walls or the like partitioning the rooms or the frequencies of radio waves, there is a possibility of the radio waves of one wireless system penetrating through the walls and interfering with other wireless systems. In particular, when a video signal with a high resolution such as a full HD video is wirelessly transmitted in real time, a communication rate is generally high, and thus an S/N ratio decreases and is weakened by interference.
In the illustrated example, a system including the video transmitter Tx1 and the video receiver Rx1 wirelessly transmits the full HD video using CH1 in Room 1. Also, a system including the video transmitter Tx3 and the video receiver Rx3 wirelessly transmits the SD video using CH1 in Room 2. Therefore, the system including the video transmitter Tx1 and the video receiver Rx1 receives the interference from the system including the video transmitter Tx3 and the video receiver Rx3. The fact that the transmission output level of the system including the video transmitter Tx1 and the video receiver Rx1 is the same as the transmission output level of the system including the video transmitter Tx3 and the video receiver Rx3 can be exemplified as a reason for this.
As a method of avoiding the interference, there is a method of lowering the transmission output of a video transmitter in addition to a method of changing a channel (changing a frequency) to be used for communication by each system. However, when the transmission output of a video receiver is simply lowered, there is a fear of the transmission output not reaching a signal level at which the video receiver may receive a signal, thereby having a considerable influence on communication quality. Also, the interference can be considered to be suppressed by changing a communication rate of the system including the video transmitter Tx3 and the video receiver Rx3 so that the communication rate is the same as a communication rate of the system including the video transmitter Tx1 and the video receiver Rx1 and by shortening a communication time of the system including the video transmitter Tx3 and the video receiver Rx3. However, as described above, when the communication rate is set to be high, the communication rate is weakened by interference. Therefore, there is a fear of the system including the video transmitter Tx3 and the video receiver Rx3 receiving the interference from the system including the video transmitter Tx1 and the video receiver Rx1.
Also, a technology for ensuring suitable communication quality by switching the number of antennas used for wireless communication based on a communication rate and an S/N ratio and effectively utilizing antenna resources is known (for example, see Japanese Unexamined Patent Application, First Publication No. 2006-54710). According to this technology, it is possible to suppress excessive transmission power when a video transmitter transmits a signal.